U.S. Pat. No. 1,892,217 discloses a gear mechanism of a progressive cavity pump or motor. This progressive cavity technology is commonly used in a pump to convert mechanical to power fluid energy, and in a motor to convert fluid energy to mechanical power. As a downhole motor, the moving energy of a drilling fluid may be converted to rotary motion to rotate a bit to drill a subterranean well. Other publications of interest including U.S. Pat. Nos. 3,084,631; 4,104,009; 4,676,725; 5,171,138; 5,759,019; 6,183,226; 6,309,195; and 6,336,796; and WO 01/44615.
Operation of a progressive cavity pump or motor utilizes an interference between the external profile of the rotor which resides inside the stator, and the internal profile of the stator. This interference allows the cavities of the pump or motor to be sealed from adjoining cavities. This seal resists the fluid pressure resulting from the mechanical pumping action, or resulting from the conversion of fluid energy to mechanical energy in a motor. This interference between the internal rotor and stator necessitates that one of or both of these components be covered with a resilient or dimensionally forgiving material which also allows the pump or motor to pass or transfer particles and other abrasive objects in either the driving  fluid (motor) or the transmitted fluid (pump). Historically, this resilient material has been provided on the interior of the stator.
The resilient material used for the stator introduces weaknesses into the operation and life of the pump/motor. Common elastomers have temperature tolerances below that of most other components in the pump or motor, e.g., metal components. Mechanical resistance of the elastomer is also of concern since high pressures are generated in the cavities of the pump/motor. These high fluid pressures and the necessary reactive forces result in significant deflection and stress in the elastomer, particularly along the rotor/stator interferences. These forces create friction which generates a large amount of heat during operation, and this heat may be very deleterious to the desired characteristics of the elastomer, and thus deleterious to the performance and life of the pump/motor.
A progressive cavity pump or motor stator is conventionally constructed by molding an elastomer with the desired spiral interior profile within a cylindrical steel tube or housing. Due to the spiral profile on the stator's inner surface, varying thicknesses of elastomer are molded between the stator inner surface and the inner surface of the metal tube to which the stator is adhered. If the heat resulting from the previously mentioned sources becomes excessive, the properties of the elastomer will more generally degrade. Elastomers have high insulative properties and thus inherently restrict the conduction of the heat generated at the rotor and stator interface from being conducted to the thermally conductive metal tube, which may then be dissipated from the pump/motor, if desired, with various cooling systems, including liquid cooling systems and exposed fin systems. The radially  thicker sections of elastomer create the greater insulative properties, and thus typically degrade faster than radially thin sections. Additionally, the high pressure experienced during operation may deflect the thicker sections of elastomer to the extent that the interference is overcome and contact with the rotor is lost. This loss of contact results in decreasing speeds for the motor and decreasing flows for the pump, resulting in poor efficiency. In addition, heat from the pump/motor operation, in some cases in conjunction with the environment in which pump/motor operates, distorts the shape of the elastomer molded to the interior of the metal tube. Elastomers have a high coefficient of thermal expansion compared to other materials used in the construction of progressive cavity pump/motor. As a result of the varying thicknesses and the relatively high thermal expansion of the elastomer, the radially thick sections distort more than the thinner sections of the stator, which results in a geometrical profile drastically different than intended, thereby hindering the proper operation of the pump/motor. This distorted profile may generate additional heat and further distort the stator profile, creating a system which rapidly contributes to its own degradation and ultimate failure.
During operation, a conventional downhole progressive cavity drill motor develops a great deal of heat due to the friction between the rotor and the stator. In addition, the flexing of the rubber profile generates heat which must be removed from the motor to prevent the elastomeric material portion of the stator from being detrimentally effected. Heat generated may be transferred to the fluid being pumped through the motor. Alternatively, the heat may be conducted through the elastomer to the stator tube or housing where the thermally conductive steel tube  then conducts heat to the drilling fluid moving along the exterior of the housing. Due to the high insulative properties of elastomeric material, heat generated along the radially thick portion of the stator profile is inhibited from effectively transferring to the thermally conductive steel tube. The center of the stator profile lobes is subjected to heat from a large percentage of its surrounding area and is the most limited in transferring this heat to the metal tube due to the thickness of the elastomeric material. With extended operation, the center of the stator profile lobes may become hard and brittle as a result of the excessive heat in this area, and the mechanical properties of the rubber or elastomer in this area are accordingly severely degraded. As a result, the stator lobe may break or “chunk out” of the stator profile. In addition, the pressure acting in the chambers between the stator and the rotor may exceed the strength of the elastomeric material, and the stator lobe may deflect from its original shape or may break or “chunk off” the stator lobe. A deflecting stator lobe degrades the pressure seal for the chambers created between the rotor and the stator.
The disadvantages of the prior art are overcome by the present invention. An improved progressive cavity pump/motor is hereinafter disclosed which overcomes many of the problems of prior art pumps and motors, including excessive build-up. The motor of a present invention is particularly well suited for use as the downhole motor in a well to rotate a bit. 